Studies showing vacuum effect occurring?

Does anybody know of any studies showing the vacuum effect occurring in cat colonies subjected to catch and kill policies? I've found plenty of studies showing that TNR reduces overall cat colony populations, but I can't find any of the vacuum effect occurring. What is the basis for the claims of this phenomenon?

That's a good question.  I found several statements citing studies but could find none of the studies themselves.  If anyone can find any of the studies themselves, I'd like to see them, too.

On the Alley Cat Allies site, there was a reference to a study about large wild cats and I know someone in Florida did a study on feral cat colonies.  The idea of a vacuum effect makes logical sense but I, too, wouldn't mind seeing some real science on it.

Yea, that is my thought. Obviously *something* is rendering catch and kill inert by the simple fact that decades of catch and kill hasn't succeeded in extirpating feral cats, but I have found any direct evidence that the "something" is the vacuum effect. It seems to be a sort of God of the gaps type of argument.

I was actually quite surprised when I found no real scientific evidence on the 'Net.  Sure hope someone else can direct me to some.

From what I can find there doesn't seem to be a scientific study of the vacuum effect in relation to feral cats.  The vacuum effect can be found in studies relating to the management of other species, either because of their impact on the environment or the opposite - managing species under threat of extinction.  But nothing specifically on feral cats... I think all the references to it in that regard may just be an extrapolation from the other studies.

I tried finding some, too.  I thought there was someone in Florida who had done a lot of research but I couldn't find anything there, either.

Mani: do you know where I might find the studies of the effect on other species?

This PDF on the vacuum effect on ferals cites a whole lot of articles and studies at the end, but I haven't looked to see how much they address the VE itself.

This is the only specific one I've found:  http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0027453&type=printable and it's talking about translocations.

To be really honest, I don't think there is any scientific study.  When you look up 'the vacuum effect' to do with animals (rather than the actual scientific principle of  'a vacuum must be filled') there are just masses of articles in relation to feral cats.  I think this is a principle that has been suggested (eg in that first PDF I've linked to) and then taken up by many feral advocacy organisations. I think that's sort of what @Ontarah is referring to with the 'God of the gaps' comment... Eradication doesn't seem to work and this seems like a valid reason why.

That study is going to take me awhile to plow through!  The vacuum effect makes logical sense to me, as does the idea that trap and euthanize does not work.

I do know that in my personal experience, we had many, many stray cats in our yard, coming and going.  I trapped most of them and fixed them.  Found homes for many of them.

The last one was just too feral and because we didn't have room inside, I built him an enclosure.  Even through he was confined, I never had a stray cat in my yard after that.  His presence kept them out.

I would see them walking in the next yard or in the woods behind us, but never saw one in the yard (or near the house) again.

When I was trapping and fixing, one neighbor and I worked together.  I did the fixing and she provided food and shelter for at least six of the cats.  I have since moved with all our cats.  My husband lives at that house (we are trying to sell it).  He's told me the other day, he's seen two of the neighbor's cats on our patio in the last few months.  So, the vacuum effect is real.

Thanks for the info, Mani!

ontarah said:

Does anybody know of any studies showing the vacuum effect occurring in cat colonies subjected to catch and kill policies? I've found plenty of studies showing that TNR reduces overall cat colony populations, but I can't find any of the vacuum effect occurring. What is the basis for the claims of this phenomenon?

Click to expand...

This was an "accidental" study of the vacuum effect---

Shooting or trapping feral cats may increase their numbers, a new study has found. "You may be inadvertently doing more damage than good," says wildlife biologist Billie Lazenby of the Tasmanian department of primary industries.

Their study was designed to compare small mammal numbers in sites where feral cats were allowed to roam free with those where the cats were reduced through culling.

"In the areas that I had tried to reduce cat numbers I recorded an increase in cat numbers," says Lazenby. "I actually had more cats running around on those sites than beforehand."

"We recorded a 75 to 211 per cent increase in the minimum number of feral cats known to be alive in the culled areas."

The results are published in a recent issue of the journal Wildlife Research

They're talking about 'low level culling', although that still constitutes an aspect of the vacuum effect.

Incidentally, I know of these people (I grew up in Tasmania) and I guess it's no surprise to say that they are not at all keen on ferals.

It stands to reason if you have good habitat that habitat will be utilized by a limited number of animals. Adjacent to that habitat is any number of the same species wanted to enter but prevented by? Dominant males, sheer numbers, competition for food or any number of things. Remove one or two of “the inner circle” and the others waiting just outside move in.
That’s how populations are limited. Nuisance species control begins by trapping and removing until the number you trap and remove daily or weekly begin to drop. If they increase as you trap then your trapping methods are not effective, usually because of the above effect. Works for mice, racoons, etc.
So if you have a cat colony that is fed, provided a somewhat safe location and spay/neuter to internally limit the population.....start removing them and those cats that are on the perimeter are says “ wow, an opening...let’s go”
As I think back the original theory was called Island Biography but has evolved since then....probably when most of you were toddlers....ha! I’m aging myself again